In recent years, due to the progressive development of the LED (Light Emitting Diode) semiconductor technique, the luminescence efficiency of chips has been greatly improved and the applications are found in all fields e.g. from a projector pen to illumination applications, and thus the application range has been greatly expanded. Furthermore, the LED has the advantages of small volume, long lifespan, low pollution, and low cost, has optical characteristics of good color saturation and dynamic color control and so on. Therefore, the LED based techniques attract more attentions.
In general, the most well-known advantages of the LED as compared with the conventional light source are power-saving, environmental friendly and small size. Also, with the presence of an AC driven LED, the LED illumination system is more competitive in use. However, a thermal problem of the LED is still one of the major subjects in the development of the LED technique. The common heat sinking methods of the LED may be classified into an active cooling type and a passive cooling type.
The Active Cooling
A forced-air or forced-liquid heat exchanging medium is used to increase the heat exchange quantity with thermo-electric coupling materials in a unit time, thereby realizing heat sinking. The design methods in practice include (1) An air cooling type: a forced convection between a cool air and a heat source is conducted under the guidance of a fan and a duct to increase the heat exchange quantity and thus reduce the temperature of the LED. However, the EMI (Electromagnetic Interference) generated by the fan and the impact of vibration of the fan may adversely affect the reliability of the chip. (2) A water cooling type: a water flow and a heat exchange quantity are increased by using a pump and a pipe to reduce the temperature of the chip, which has a simple and effective configuration, but the EMI generated by the pump, an expansion and contraction of a coolant, and a leakage problem should be noted. (3) A thermal-electric coupling type: based on the characteristic of a thermal-electric coupling effect of the semiconductor, a cold end of a thermoelectric cooling chip supplied with an electrical energy to reduce the temperature of the LED module, which has the defect of power consumption.
The Passive Cooling
A natural convection, conduction, and radiation manners are boosted with a physical structure to conduct the heat exchange. This manners have been widely applied in the design of a heat slug of an electronic device and is the most economical and durable design.